The present invention relates to a method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, a method of measuring the diffusion coefficient, and an MRI (Magnetic Resonance Imaging) apparatus. More specifically, the present invention relates to a method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, the method being capable of determining appropriately the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of nerve fibers, and a method of measuring the diffusion coefficient and an MRI apparatus, the method and apparatus being capable of measuring accurately the diffusion coefficient of nerve fibers.
The diffusion coefficient of nerve fibers is known to differ in value between the direction along the fiber direction and the direction orthogonal to the fiber direction.
Therefore, it is necessary for the measurement of the diffusion coefficient of nerve fibers to apply a gradient magnetic field for the diffusive motion detection in the direction along the fiber direction or the direction orthogonal to the fiber direction. Otherwise, a measured value, which is neither a diffusion coefficient in the direction along the fiber direction nor a diffusion coefficient in the direction orthogonal to the fiber direction, is meaningless.
On this account, conventionally, the doctor or technician has inferred the fiber direction of nerve fibers based on one""s experience by viewing the ordinary MRI image (a monochrome display of the proton density image) and determined the direction of diffusive motion detecting gradient magnetic field to be applied in accordance with the inferred fiber direction.
However, it is problematic in that the fiber direction of nerve fibers cannot necessarily be inferred correctly from the MRI image.
It is an object of the present invention to provide a method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, the method being capable of determining appropriately the direction of diffusive motion detecting gradient magnetic field (Motion Probing Gradient) to be applied for the measurement of the diffusion coefficient of nerve fibers, and a method of measuring the diffusion coefficient and an MRI apparatus, the method and apparatus being capable of measuring accurately the diffusion coefficient of nerve fibers.
At a first viewpoint, the present invention provides a method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, the method being characterized by producing, by being based on data which is collected by sequential application of diffusive motion detecting gradient magnetic fields along at least two axes out of three orthogonal axes, at least two diffusion-weighted images which correspond to the application axes, composing an image from the diffusion-weighted images by allotting different display colors thereto, displaying the composed image or the intensity-inverted version thereof, and determining the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of a region of interest on the composed image or the intensity-inverted image based on the hue of the region of interest.
The diffusive motion detecting gradient magnetic field application direction determining method of the first viewpoint yields at least two diffusion-weighted images of different application axes, and due to the anisotropy of diffusion coefficient of nerve fibers, diffusion-weighted images of nerve fibers are displayed differently from each other. When an image is composed from the diffusion-weighted images, with different display colors being rendered thereto, the resulting nerve fiber image has hues which depend on the directions of fibers. Accordingly, it is possible to determine the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of a region of interest based on the hue of the region of interest.
At a second viewpoint, the present invention provides a method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, the method being characterized by producing, by being based on data which is collected by sequential application of diffusive motion detecting gradient magnetic fields along three orthogonal axes, three diffusion-weighted images which correspond to the application axes, composing an image from the diffusion-weighted images by allotting different display colors thereto, displaying the composed image or the intensity-inverted version thereof, and determining the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of a region of interest on the composed image or the intensity-inverted image based on the hue of the region of interest.
The diffusive motion detecting gradient magnetic field application direction determining method of the second viewpoint yields three diffusion-weighted images of different application axes, and due to the anisotropy of diffusion coefficient of nerve fibers, diffusion-weighted images of nerve fibers are displayed differently from each other. When an image is composed from the diffusion-weighted images, with different display colors being rendered thereto, the resulting nerve fiber image has hues which depend on the directions of fibers. Accordingly, it is possible to determine the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of a region of interest based on the hue of the region of interest.
At a third viewpoint, the present invention provides a method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, the method being derived from the diffusive motion detecting gradient magnetic field application direction determining methods of the foregoing viewpoints and characterized in that an operating person sets a region of interest by specifying a frame of region or a center point of a frame of region on the composed image or the intensity-inverted image.
The diffusive motion detecting gradient magnetic field application direction determining method of the third viewpoint enables easy setting of a region of interest by an operating person who specifies a frame of region or a center point of a frame of region on the composed image or the intensity-inverted image.
At a fourth viewpoint, the present invention provides a method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, the method being derived from the diffusive motion detecting gradient magnetic field application direction determining methods of the foregoing viewpoints and characterized by determining the direction of application of gradient magnetic field for the detection of diffusive motion based on the relation between the hue of the region of interest in terms of an intensity vector (r,g,b) of t three primary colors of red, green and blue and the direction of diffusive motion detecting gradient magnetic field in terms of a directional vector (x,y,z):
x=r/(r+g+b)
y=g/(r+g+b)
z=b/(r+g+b).
The diffusive motion detecting gradient magnetic field application direction determining method of the fourth viewpoint enables easy evaluation of the directional vector indicative of the direction of diffusive motion detecting gradient magnetic field based on the intensity vector of the three primary colors.
At a fifth viewpoint, the present invention provides a method of measuring the diffusion coefficient of a region of interest by application of diffusive motion detecting gradient magnetic field in a direction which is determined based on the diffusive motion detecting gradient magnetic field application direction determining methods of the foregoing viewpoints.
The diffusion coefficient measuring method of the fifth viewpoint enables accurate measurement of the diffusion coefficient of a region of interest by application of diffusive motion detecting gradient magnetic field in the direction which is determined based on the diffusive motion detecting gradient magnetic field application direction determining methods of the foregoing viewpoints.
At a sixth viewpoint, the present invention provides an MRI apparatus characterized by comprising a diffusion-weighted image producing means which applies diffusive motion detecting gradient magnetic fields sequentially along at least two axes out of three orthogonal axes thereby to collect data and produces at least two diffusion-weighted images which correspond to the application axes, a composed image display means which composes an image from the diffusion-weighted images by allotting different display colors thereto and displays the composed image or the intensity-inverted version thereof, a diffusive motion detecting gradient magnetic field application direction determining means which determines the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of a region of interest on the composed image or the intensity-inverted image based on the hue of the region of interest, and a diffusion coefficient measuring means which measures the diffusion coefficient of the region of interest by application of diffusive motion detecting gradient magnetic field in the determined direction.
The MRI apparatus of the sixth viewpoint can carry out properly the diffusion coefficient measuring method of the fifth viewpoint.
At a seventh viewpoint, the present invention provides an MRI apparatus characterized by comprising a diffusion-weighted image producing means which applies diffusive motion detecting gradient magnetic fields sequentially along three orthogonal axes thereby to collect data and produces three diffusion-weighted images which correspond to the application axes, a composed image display means which composes an image from the diffusion-weighted images by allotting different display colors thereto and displays the composed image or the intensity-inverted version thereof, a diffusive motion detecting gradient magnetic field application direction determining means which determines the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of a region of interest on the composed image or the intensity-inverted image based on the hue of the region of interest, and a diffusion coefficient measuring means which measures the diffusion coefficient of the region of interest by application of diffusive motion detecting gradient magnetic field in the determined direction.
The MRI apparatus of the seventh viewpoint can carry out properly the diffusion coefficient measuring method of the fifth viewpoint.
At an eighth viewpoint, the present invention provides an MRI apparatus which is derived from the MRI apparatus of the foregoing viewpoints and characterized by further including a region setting means which sets a region of interest based on the operation by an operating person who specifies a frame of region or a center point of a frame of region on the composed image or the intensity-inverted image.
The MRI apparatus of the eighth viewpoint can readily set a region of interest based on the operation by an operating person who specifies a frame of region or a center point of a frame of region on the composed image or the intensity-inverted image.
At a ninth viewpoint, the present invention provides an MRI apparatus which is derived from the MRI apparatus of the foregoing viewpoints and characterized in that the diffusive motion detecting gradient magnetic field application direction determining means determines the direction of application of gradient magnetic field for the detection of diffusive motion based on the relation between the hue of the region of interest in terms of an intensity vector (r,g,b) oft three primary colors of red, green and blue and the direction of diffusive motion detecting gradient magnetic field in terms of a directional vector (x,y,z)
xe2x80x83x=r/(r+g+b)
y=g/(r+g+b)
z=b/(r+g+b).
The MRI apparatus of the ninth viewpoint can readily evaluate the directional vector indicative of the direction of diffusive motion detecting gradient magnetic field based on the intensity vector of the three primary colors indicative of the hue.
According to the inventive method of determining the direction of application of diffusive motion detecting gradient magnetic field, it is possible to determine appropriately the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of diffusion coefficient.
According to the inventive diffusion coefficient measuring method and MRI apparatus, it is possible to measure accurately the diffusion coefficient of nerve fibers.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.